Abstract
Seahorses are considered one of the most iconic examples of a monogamous species in the animal kingdom. This study investigates the relationship between stocking density and mating and competitive behavior from the context of the field biology of the dwarf seahorse, Hippocampus zosterae (Jordan & Gilbert). Animals were housed in 38 liter tanks at a range of densities and sex ratios (from 2–8 animals per tank), and their reproductive and other social behaviors were monitored from tank introduction through copulation. At low tank densities and even sex ratios but comparatively high field densities, frequency of both mating and competitive behaviors was low in trials. A higher level of males in tanks across all densities increased competition, activity levels, and aggression leading to egg transfer errors and brood expulsion, resulting in lower reproductive success. Across seahorse species, mean and maximum wild densities were consistently lower than those used in ex situ breeding, with adult sex ratios that were significantly female biased. However, significant variation exists in wild seahorse densities across species, with higher densities detected in focal/mark recapture studies and on artificial habitat structures than reported with belt transect sampling techniques. Interchange of knowledge gained in both aquarium and wild contexts will allow us to better understand the biology of this genus, and improve reproduction in captivity. Interpreting ex situ reproductive behaviors of seahorses within various densities reported from natural populations will help us predict the impact of conservation efforts and increase the likelihood of long-term persistence of populations for this threatened genus.
Highlights
Maladaptive behaviors have been observed in captivity in animals brought in from the wild, often associated with holding and/or capture stress [1,2,3]
This pattern was marked on the day of copulation, when the rate of social activity increased by 160% (Dunnett’s test with 1:1 treatment as control, both 2:1 and high density group p
High density tanks displayed an increase in time to copulation of 31%, compared to the 1:1 control tanks, and over the active time on that day, an average of 3 fish were engaged in courtship or competitive behaviors, compared to the lowest density treatments which had a shorter day of copulation and an average of only 1.5 fish active per social interaction
Summary
Maladaptive behaviors have been observed in captivity in animals brought in from the wild, often associated with holding and/or capture stress [1,2,3]. Much of the research on behavior in captivity has focused on animals bred in aquaria, with the expectation that either genetic or epigenetic factors were involved in the development of behaviors that lead to lower. Density effects on seahorse reproductive behavior played a role in in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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